Apparatus for coating metal onto metal by vaporizing the coating



Oct. 27, 1959 P. w. PATTON ETAL 2,910,039

APPARATUS FOR COATING METAL ONTO METAL BY VAPORIZING THE COATING 2 Sheets-Sheet Filed June 21, 1956 w w m f w e R e W Source Valve Open P/bfe Heafer 0n Oct. 27, 1959 P. w. PATTON ETAL 2,910,039

' APPARATUS FOR COATING METAL omo METAL BY VAPORIZING THE COATING 2 Sheets-Sheet 2 Filed June 21, 1956 APPARATUS FOR COATING IVIETAL ONTO METAL BY VAPORIZING THE COATING Paul W. Patton, Valley Falls, R.I., and Robert H. Kelly,

Wellesley, Mass, assignors to National Research Corpltliration, Cambridge, Mass., a corporation of Massac usetts Application June 21, 1956, Serial No. 592,853

2 Claims. (Cl. 118-49) This invention relates to coating and more particularly to vacuum deposition processes and apparatus which are particularly useful in coating a substrate with selenium.

Prior art methods of coating with selenium have produced coated products which often have had poor quality and which have always involved a relatively great expense.

Accordingly, it is a principal object of the instant invention to provide improved apparatus for uniformly coating a substrate with selenium at a reasonable cost.

Another object of the present invention is to provide improved apparatus for uniformly coating a relatively large number of objects both cheaply and at high speed.

The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangements of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

Fig. 1 is a diagrammatic, schematic illustration of one preferred embodiment of the invention; and

Fig. 2 is a fragmentary enlarged sectional view of a portion of Fig. 1 taken along the lines 2-2.

The present invention is particularly directed to improved apparatus for the vapor deposition coating of substrates with selenium. For convenience of illustration, the invention will be described initially in connec tion with a preferred form of apparatus designed for the coating of aluminum plates with a uniform layer of vapor-deposited selenium to be subsequently formed into rectifiers. This specific embodiment of the invention is given for illustrative purposes only and is not to be construed as limiting the scope of the invention.

As heretofore practiced, the coating of such rectifier plates with selenium by vapor deposition techniques, even when carried out with extreme care, has left much to be desired. Oftentimes, although all reasonable care was exercised during the coating operation, large numbers of selenium-coated articles have had to be classed as rejects due to the poor quality of the selenium coating. Additionally, complicated jigs have been employed to hold the plates during coating. These jigs have necessitated expensive loading and unloading operations and have enormously complicated the problem of uniformly heating the plates during coating. Equally,

United States Patent C if the design of jigs which would not cast a shadow on the plate has complicated the whole problem of plate support.

In one preferred embodiment of the invention, the principal problems of the prior art are overcome by providing a plurality of vacuum chambers in each of which a plate to be coated is placed below a source of selenium vapors. The plate is supported in the chamber by a suitable carrier which need engage only the back side ICC 'of the plate since the plate is held in position by gravity. The individual vacuum chambers-are preferably mounted on a rotary support,'such as a carousel, so that each chamber is arranged to be sequentially brought to a loading and unloading position where a single operator can supervise a large number of coating chambers. Ac-

cordingly, as each coating chamber approaches the operaerably automatically, and the coating chamber is moved I away from the operator to startits cycle, the pumpdown of the chamber being started as soon as the chamber has been reclosed.

The quality of such a selenium coating is largely dependent upon the temperature of the aluminumplate and the temperature of the selenium coating vapor, In the instant invention, the temperature gradient across'the plate can be maintained at a variance of less than 1 C. from any predetermined temperature within the range C. to 200 C. This is preferably accomplished by utilizing as heating units a relatively large number of resistance-heated rods which are preferably positioned close to the plate carrier and above the carrier so as to radiate heat directly to the surface to be coated. The temperature of these rods and, therefore, the temperature of the plate surface can be easily and closely regulated,

and the large number of rods insures a substantially uniform transfer of heat from the rods to the substrate across the entire surface to be coated. As a result, it is possible to maintain a gradient of less than 1 C. across the plate at any desired temperature in the range between 100 C. and 200 C. In a similar manner, a plurality of resistance-heated rods are provided within the walls of the crucible supporting the molten selenium. These rods serve as heating units and maintain a closely controlled high temperature in the selenium and its vapors. Accordingly, the vapors and the plate are maintained at optimum temperatures for the particular type of coating.

To insure complete uniformity of coating, it is preferred that relative horizontal motion be provided between the plate and the selenium vapor source. In a preferred embodiment, the plate carrier is arranged to be moved back and forth in a horizontal plane beneath the source of selenium vapors. This movement is a critical factor in obtaining coatings of uniform depth. By moving the plate at a predetermined rate back and forth in the vapor stream while maintaining a substantially constant spacing between the plate and the source of selenium vapors, all areas of the plate are exposed to the coating vapor for substantially the same lengthof time. A uniform coating across the entire surface is thereby obtained.

The selenium vapor source, due to its relatively high heat capacity, is preferably maintained at a constant temperature during the whole coating cycle, even during the times when the coating chamber is open to the atmosphere. during times when the plate is not being coated, the selenium vapor source is provided with a valve for closing the vapor passage during most of the operating cycle.

Referring now to the drawings, there are indicated in Figs. 1 and 2 schematic, diagrammatic representations of one preferred embodiment of the invention. Fig. 1 is a plan view of a carousel incorporating a plurality of vacuum coating chambers 10, only three of these coating chambers 10 being shown and only one of these chambers 10 and its associated pumping system 12 being described in detail. Normally the total carousel installation would have on the order of a dozen coating chambers and a dozen associated vacuum pumping systems.

Patented Oct. 27, 1959 In order to prevent loss of selenium vapors These two units (coating chamber and pumping system) are connected together and ride on a track, a portion of which is illustrated at 14. Each coating unit is preferably driven by means of a radial arm 16 operating around an .axis 18. The coating. chamber is provided with a door 20, shown in Fig. 1 as-being open, and is arranged to be isolated from the pumping system by means of a valve 22 in the vacuum pumping line 23 which connects the vacuum pumping system 12 with the vacuum coating chamber 10. A second valve 24 is employed for periodically breaking the vacuum in the coating chamber. An aluminum plate to be coated with selenium is schematically indicated at 26, the plate being shown in dotted lines in its coating position under a selenium vapor source 28; For-simplicity of illustration, the

previously mentioned plate heaters, selenium source heater and selenium source valve are eliminated from Fig. 1.

Referring now to Fig. 2, there is shown an enlarged, sectional view, still largely schematic, of an individual coating chamber, where like numbers refer to like elements in Fig. l. The plate 26 to be coated with selenium is positioned on a carrier 3:) which is arranged to travel on a track 32. The carrier preferably has closely fitting edge supports 31 which act to prevent travel of selenium vapors to the back side of the plate. The central portions of the plate are preferably supported by knife edges 33 which prevent undue cooling of the substrate by its support and thus permit the attainment of a substantially uniform temperature over the whole upper surface of the plate. The carrier also includes a rack 34 on the bottom side thereof, this rack being engaged by a pinion 36 and driven by a motor 38. A plurality-of heaters 40 are positioned above the path of travel of the plate 26 and are positioned to heat its upper surface both While it is stationary and during its travel in the coater. The selenium vapor source 28 comprises an inner crucible 42 for holding the molten selenium 44. A transverse slit 46 is provided in the crucible 42 to permit escape of selenium vapors in a downwardly direction when a valve 48 is moved from the position shown in full lines to the 7 position shown in dotted lines where an opening 59 in the valve 48 is aligned with the slot 46. A plurality of heating elements 52 surround the inner crucible 42 sons to maintain this crucible and its contained selenium at a predetermined elevated temperature. A layer of insulating material 53 preferably surrounds the heating elements. The top portion 59 of the selenium vapor source is preferably removably secured thereto to permit periodic replenishing of the selenium. The valve 48 is aranged to be moved by means of a connecting rod 54 engaged by a cam 56 suitably driven by a motor 53. Shields 60 are preferably provided above the heaters in a position to be maintained relatively hot so as to prevent condensation of selenium vapors on shields 60. This is desirable in order to prevent selenium fragments from falling from the chamber roof onto the aluminum plates 26 during treatment. shown) are provided so as to measure the temperature of the heating elements 40, the temperature of the heating elements 52, the temperature of the selenium 44 and the temperature of the plate 26. These are preferably connected to suitable automatic controllers (not shown) for regulating the power input to the various heaters to maintain the various temperatures within the necessary preset close tolerances.

The operating cycle of the equipment can be best understood by referring again to Fig. 1 (as 'well as Fig. 2). With the coater at the loading station shown, the door is open, the coater is empty, and the selenium heaters 52 have been turned on to heat the selenium up to its vaporizing temperature (e.g., 275 C.). The selenium vapor valve 48 is closed to prevent escape of selenium vapors and the plate carrier 30 is in the left-hand position shown in Fig. 2. After the plate has been inserted by the A number of thermocouples (not operator, the door is closed, the vent valve 24- is closed, and valve 22 in the vacuum pumping line is opened. These operations are preferably accomplished automatically by suitably positioned cams along the path of travel of the selenium coater as it moves from the loading station to the vent station on its path of travel around the carousel. This motion is preferably intermittent to give the operator maximum time to load the coating chamber, to replenish selenium as needed, and to remove any scum from the surface of the molten selenium in source 23. The plate heater 40 is then turned on and the plate is heated up to the desired coating temperature, the heater maintaining this temperature as soon as it has been reached. By the time the pressure in the coating chamber has been adequately reduced (e.g., to a pressure on the order of 0.001 millimeter Hg abs.), the plate will have been heated to an adequate coating temperature (140 C., for example) and the coating operation can begin. The plate 26 is in turn reciprocated under the selenium vapor source by a suitably operating motor 38. At this time, the source valve 48 is moved to the right so as to align opening 56 with the slot 46, thereby permitting a stream of selenium vapors to pass downwardly onto the exposed hot surface of the plate 26. This coating continues for a given time (3 minutes, for example) so as to provide a selenium coating of about 0.0025 inch, whereupon valve 48 is closed and the plate heaters are preferably turned off to permit cooling of the plate 26. Vacuum pumping valve 22 is next closed, the vacuum breaking valve 24 is then opened to permit opening of the door 29, and the finished plate is unloaded, the coater now being ready to receive another plate for identical treatment.

While the present invention is particularly designed for the production of selenium rectifier plates, it is also applicable to numerous other uses.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus for coating a substrate with selenium by vapor deposition techniques which comprises a plurality of coating units arranged to be moved in sequence past a plurality of operating stations, each unit comprising a vacuum-tight coating chamber, a vacuum-tight closure which can be opened for permitting loading of said chamber when said chamber is at a loading station, means for evacuating said chamber, a valve for venting said chamber to atmosphere, means for providing a crucible containing selenium within said chamber, said crucible having at least one chamber and at least one long narrow slot, which slot serves to direct selenium vapor in a downwardly direction toward a substrate to be coated, means for heating said crucible and thereby vaporizing said selenium, a second valve preventing escape of vapors from said vaporizing means, means for periodically opening said second valve during travel of the coating unit along a predetermined portion of said path, means for maintaining said substrate at a predetermined temperature, and means for creating relative movement between said source of selenium vapor and said substrate during the time when said second valve means is open to permit travel of selenium vapors tovalve for isolating said evacuating means from said chamber prior to arrival of said chamber at the loading station, a second valve for venting said chamber to atmosphere after said first valve is closed, means for providing a crucible containing said coating material Within said chamber, means for heating said crucible and thereby vaporizing said coating material, a third valve preventing escape of vapors from said vaporizing means,

means for periodically opening said third valve during valve is open to permit travel of coating material vapors toward the substrate.

References Cited in the file of this patent UNITED STATES PATENTS 2,273,941 Dorn Feb. 24, 1942 2,363,781 Ferguson Nov. 28, 1944 2,378,476 Guellich June 19, 1945 2,408,614 Dimmick Oct. 1, 1946 2,426,377 Smith Aug. 26, 1947 2,445,310 Chilowsky July 20, 1948 2,503,571 Wehe Apr. 11, 1950 2,740,928 Ward Apr. 13, 1956 2,767,682 Smith Oct. 23, 1956 

1. APPARATUS FOR COATING A SUBSTRATE WITH SELENIUM BY VAPOR DEPOSITION TECHNIQUES WHICH COMPRISES A PLURALITY OF COATING UNITS ARRANGED TO BE MOVED IN SEQUENCE PAST A PLURALITY OF OPERATING STATIIONS, EACH UNIT COMPRISING A VACUMM-TIGHT COATING CHAMBER, A VACUMM-TIGHT CLOSURE WHICH CAN BE OPENED FOR PERMITTING LOADING OF SAID CHAMBER WHEN SAID CHAMBER IS AT A LOADING STATION, MEANS FOR EVACUATING SAID CHAMBER, A VALVE FOR VENTING SAID CHAMBER TO ATMOSPHERE, MEANS FOR PROVIDING A CRUCIBLE CONTAINING SELENIUM WITHIN SAID CHAMBER, SAID CRUCIBLE HAVING AT LEAST ONE CHAMBER AND AT LEAST ONE LONG NARROW SLOT, WHICH SLOT SERVES TO DIRECT SELENIUM VAPOR IN A DOWNWARDLY DIRECTION TOWARD A SUBSTRATE TO BE COATED, MEANS FOR HEATING SAID CRUCIBLE AND THEREBY VAPORIZ- 